Wireless communication systems are widely deployed to provide various kinds of communication services such as voice and data services. Generally, these communication systems are multiple access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth and transmit power). Examples of multiple access systems include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency-division multiple access (SC-FDMA) system, and a multi-carrier frequency division multiple access (MC-FDMA) system.
Device-to-device (D2D) communication represents a communication scheme of establishing a direct link between user equipments (UEs) such that the UEs directly exchange services such as voice and data without assistance from an evolved NodeB (eNB). D2D communication may include UE-to-UE communication and peer-to-peer communication. In addition, the D2D communication scheme may be applied to machine-to-machine (M2M) communication, machine type communication (MTC), etc.
D2D communication is considered as one measure to address load to an eNB according to rapidly increasing data traffic. For example, according to D2D communication, since devices exchange data directly, not through an eNB as in the conventional wireless communication systems, network load may be reduced. In addition, with introduction of D2D communication, the procedures for the eNB may be simplified, power consumption of devices participating in D2D communication may be reduced, data transmission rate may increase, the capacity of a network may increase, load may be distributed, and cell coverage may be extended.